Ethylene-vinyl alcohol copolymer (hereinafter also abbreviated as EVOH) can be melt-molded, and has excellent gas barrier properties against oxygen or carbon dioxide gas. For this reason, a multilayered structure including a layer made of EVOH and a layer made of a thermoplastic resin having excellent moisture-resistance, mechanical properties or the like (e.g., thermoplastic polyester; hereinafter thermoplastic polyester may be abbreviated as PES) is utilized for various molded products (e.g., films, sheets, bottles, containers, etc.) that require gas barrier properties. For example, such multilayered structures are used in various fields as a multilayered container, in particular, in the form of bags, bottles, cups, pouches, etc. For example, they are widely used in such fields as foods, cosmetics, medicines, toiletries and the like.
Such a multilayered container has good barrier properties against oxygen, carbon dioxide gas, and the like. However, its permeability of gases such as oxygen is not exactly zero, unlike metals used for cans, etc. and glass used for bottles, etc. but still permits transmission of gas in an amount that cannot be neglected. In particular, for containers of foods, the degradation of food contents due to oxidation when the food is preserved for a long time is of great concern. Therefore, improvement of the oxygen barrier properties is strongly desired.
Furthermore, when filling the contents into a container, oxygen may be mixed in the container together with the contents. When the contents are susceptible to oxidization, even a trace amount of oxygen may degrade the quality of the contents. In order to prevent this, providing a material of the container with an oxygen scavenging function has been proposed. In this case, oxygen that might enter the container from the outside can be scavenged, so that the gas barrier properties of a packaging material also can be improved.
For example, as the method of providing the oxygen scavenging function to the EVOH that constitutes a packaging material, the following methods are known: (1) An oxidation catalyst such as a transition metal is added to the EVOH to make the EVOH susceptible to oxidation, thereby providing the EVOH with the oxygen scavenging function (Japanese Laid-Open Patent Publication (Tokkai) No. 4-211444); (2) A resin composition mainly comprising polyolefin and an oxidation catalyst, that is, polyolefin in a state susceptible to oxidation, is dispersed in the EVOH, thereby providing the EVOH with the oxygen scavenging function (Japanese Laid-Open Patent Publication (Tokkai) No. 5-156095); and (3) EVOH, polyolefin, and an oxidation catalyst are blended to make the EVOH and polyolefin susceptible to oxidation, thereby providing the oxygen scavenging function (Japanese Laid-Open Patent Publication (Tokkai) No. 5-170980). However, method (1) fails to provide sufficiently improved oxygen barrier properties. Methods (2) and (3) have the disadvantage that the transparency is impaired significantly.
Furthermore, in multilayered containers, especially when no adhesive resin layer is provided between the layers and the container filled with a drink or food is subjected to an impact caused by, for example, being dropped, delamination between the thermoplastic resin layer (e.g., PES layer) and the EVOH layer is likely to occur, which causes a large problem in the appearance.